Stochastically Perturbed Parmaters [SPP]
Andrew Singleton
Preliminary point verification for SOP 1
What parameters do we perturb?
- Cloud thickness threshold for shallow / deep convection
- Cloud ice content impact on cloud thickness
- Ice nucleii concentration
- Saturation limit sensitivity for condensation*
- Kogan autoconversion speed
- Kogan sub grid scale (cloud fraction) sensitivity*
- Impact of graupel on radiation
- Impact of snow on radiation*
- Top entrainment efficiency
- Stable conditions length scale
- Asymptotic free atmosphere length scale
However… This Presentation is not as advertised!
- Original reference runs had problems with warm perturbed members in winter and dry perturbed members in summer
- Original reference did not include modelling of snow on sea ice
- Some default physics parameter values are changed for SPP
- The reference is re-run with
- 6 perturbed members
- No surface data assimilation for perturbed members
- Snow on sea ice modelling
- Physics parameter defaults changed
Point verification for (near) surface parameters
2m Temperature

2m Temperature [members]

2m Temperature “first guess”

Temperature [upper air]

2m Humidity

2m Humidity [members]

Relative Humidity [upper air]

10m Wind Speed

10m Wind Speed [members]

Wind Speed [upper air]

6h Precipitation

6h Precipitation [members]

Total Cloud Cover

Total Cloud Cover [members]

Geopotential Height [upper air]

Summary
- Warming of perturbed members reduced
- Night time wet bias removed in perturbed members
- Large positive bias in initial cloud cover for perturbed members removed
- Overall reduction in spread for all parameters
- Less spread throughout atmosphere